Traditionally fallowing is a method to improve soil condition between cultivation periods. Decreased soil disturbance may decrease erosion, increase soil carbon sequestration and thus soil organic matter content, which profit cultivation. The climate benefit trend is sustained for the period of time the soil is fallowed. (Paustian et al. 2006). Thus, in the way fallowing is generally perceived, as a short term phase for cultivated soil, it is not suitable for long term GHG mitigation. For climate change mitigation fallowing is supposed to be more permanent solution for the land, as shorter fallow period is not expected to have difference for climate change. Thus also we expect that the fallowing is a permanent choice.
There are two distinctive ways to fallow the land. On bare fallow the soil is kept without vegetation either mechanically or chemically. On green fallow the soil is kept as undisturbed as possible and with vegetation cover. Vegetation on green fallow can either be annual or perennial. Perennial fallow is normally used if the fallowing is planned to continue several years. Fertilization is not normally needed especially if nitrogen binding vegetation such as legumes or clovers is sowed. (Hyytiäinen & Hiltunen 1992, 78-79.) Although the both systems are introduced as fallowing, they have very different
environmental performance, profiting green fallow. Thus when talking about climate mitigation in terms of fallowing or set aside, is green fallow generally in question.
Green fallow vegetation restrains erosion, decreasing nutrient runoff to water systems and increase soil carbon content (Hyytiäinen & Hiltunen 1992, 78; Heinonen, Hartikainen, Aura, Jaakkola & Kemppainen 1992, 314). It has also been noticed to decrease nitrous oxide emissions compared with croplands, which is probably due to absence of nitrogen fertilization (Ruser et al. 2001). On the other hand using legumes such as green fallow vegetation might increase N2O emissions (Nieder & Benbi 2008, 207). Bare fallow has not
the same capacity to decrease greenhouse gas emissions due to absence of vegetation and continuous mechanical or chemical soil disturbance (Heinonen et al. 1992, 314; Syväsalo et al. 2004; Regina, Syväsalo, Hannukkala & Esala 2004; Lohila, Aurela, Regina, & Laurila 2003).
Table 6 presents the emission fluxes from fallowed fields. Organic soil continue to be a source of carbon dioxide and the emission rate is expected here to be constant, although it is possible that the emission flux changes in the course of time. Maljanen et al. (2007) have studied abandoned organic crop fields (cultivation ended 30 to 40 years earlier) growing for example grasses and have ended up with results of annual net ecosystem exchange (NEE) of 3 200 kg CO2/ha. As we are interested in the long term impact of green fallow, emissions
fluxes are from abandoned fields probably more robust than congruent emissions from recently ceased crop field.
Similar experiment studies are not available for mineral soils but Freibauer, Rounsevell, Smith and Verhagen (2004) suggest that set-aside fields would sequester carbon similarly as no-till fields. Thus we have derived carbon dioxide emissions from this assumption using carbon sequestration rate provided by Lal et al. 1999 (500 kg C/ha/year, ~1835 kg CO2/ha/year) for no-till fields. The sequestration rate is accounted from conventionally
managed fields, making clay and silt soils a sink of carbon dioxide. To calculate the long term impact of fallowing, we expect that the carbon accumulation is maintained for 25 years. The accumulation decrease during time as described in equation (8). Due to lack of data
about nitrous oxide and methane emissions from mineral green fallowed soils, we assume later that the emission flux to be the same as for organic soils.
Table 6. Climate emissions of fallowed soils. Negative value signify emission sink.
GHG gas Clay Soil Silty soil Organic
Green fallow CO2 -263b* -1053b* 3240a N2O nd. nd. 8.2a CH4 nd. nd. -1.7a CO2-eq. > -263 > -1053 5641 Bare fallow CO2 6100c 8700c 7900d N2O 5,5-7,8e 1,6-3,5f 6,5-7,1f CH4 0,19-0,29g -1,94g -0,34g CO2-eq. 8088 9436 9920 a
Maljanen et al. (2007); bLal et al. (1999); cLohila (2008); dMaljanen et al. (2004); eSyväsalo et al. (2004); fMartikainen et al. (2002); gMaljanen (2003b)
* Sequestration rate estimated from 25 years following the principle of reducing sequestration capacity.
We analyse the social welfare of green fallow by including private returns and environmental costs or benefits from the fallowing period. We expect that the annual costs from establishment and maintenance are -44 €/ha, and private returns zero. Although fallowing is suggested to improve soil quality and thus possibly improve crop cultivation productivity in future, we assume that crop cultivation is not continued later but the land is on farmer’s point of view permanently fallowed and productivity improvements indifferent.
For nutrient runoff we use estimates by Turtola (1993) who has studied different fallowed parcels in Finland during several years. Although fallowing decrease nitrogen and phosphorus runoff, are the rates nevertheless relatively high. Nitrogen runoff is measured to be an average 5 kg/ha and total phosphorus about 0,9 kg/ha (table 7).
In addition to climate and nutrient runoff, we also expect that fallowed field is valued for its landscape. To describe the value of rural landscape, we use the LFA (less favourable area)
payment. LFA is provided in European Union for farmers on areas where cultivation would not be otherwise profitable. Thus LFA describes the benefits of these creating from other reasons than effective crop production, such as rural area vitality and biotopes of rural environment. LFA payment was 169€/ha in 2007 for forage barley.
Green fallow or grass cultivation is suggested to be a better solutions for GHG mitigation than for example afforestation, which has additional impacts on biodiversity and landscape. But in any case, restricting cultivation has socio-economic impacts which would probably become unevenly distributed. According to Lehtonen, Peltonen and Sinkkonen (2006), restricting crop cultivation on peatlands in Finland, allowing only perennial crops, would have the strongest impact on Lapland, where 40 % of the peatland under cultivation are located. Nevertheless, climate policy directed on peatlands would reallocate crop and grass production to more productive soils and would affect agricultural income in Northern Finland only slightly. There is also a possibility that agricultural income would eventually increase compared with the base line. In addition another, environmental and economic benefits would create as a consequence. (Lehtonen et al. 2006.)
5 Comparison of farmland use options
In this chapter we compare the results in order to determine the socially optimal land allocation and production intensities. Later also optimal policies to obtain the socially optimal solutions are discussed. For crop cultivation we examine four different policy scenarios in terms of the environmental impacts. The policy schemes take into account either only carbon dioxide emissions or all CO2-eq. emissions including nitrous oxide and
methane emissions. Further these are treated with and without nutrient runoff. This is because the presumption is, that the policy should be directed so that all externalities are taken into account in order to obtain the maximum social welfare, but in reality this is not always possible to attain. Thus we view the solution in which the policy is considered to take into account all externalities and when it is not. Furthermore, we define the policy related social welfare and complement it by a welfare measure.
Although the main objective of the study is to analyse the social welfare, we do also view the privately optimal solution to compare the difference between input uses and land allocation in the privately and socially optimal solution and to derive the optimal policies.